This invention relates generally to optical thermal imaging techniques and, more particularly, to techniques for detecting defects in semiconductor devices or structures. Semiconductor devices are, of course, widely used in a variety of contexts and are typically fabricated as integrated circuit (IC) chips, or as IC wafers containing large arrays of semiconductor devices. Cracks in a semiconductor device have the potential to severely limit its performance. Once a crack has begun, it is highly probable that it will propagate over time to develop into a more significant crack. Therefore, it is important to detect not only large cracks but also small ones.
Currently, cracks in semiconductor devices are inspected mainly by a thermal method. With an infrared camera, an inspector can see the change in temperature in the device as it is powered up electrically. A “hot” spot may be indicative of the presence of a crack. Typical electrical failures occur when there is temperature rise of over 50° C. By this technique, problems can be detected well in advance of a failure, but such a thermal inspection method can best be used for detection of large cracks, but not for small ones. In addition, a thermal method is an invasive and slow process.
U.S. Pat. No. 6,806,249 describes an optical method for the inspection of a semiconductor wafer using a brightfield and darkfield arrangement. The method appears to be applied mainly to detect the presence of small particles on the surface of a wafer.
Most semiconductor devices and arrays have multiple layers of material that render optical inspection difficult. It will be appreciated, therefore, that there is a need for a method for detection of micro-cracks and other defects that is quick, non-invasive and may be used at the array level as well as the device level. The present invention meets and exceeds these requirements.